Heart transplantation is now an acceptable treatment alternative for select patients with end-stage heart disease. The five year survival for transplant recipients is over 70%. Unfortunately up to 40% of these transplant recipients will develop transplant coronary artery disease, a vasculopathy which is diffuse but generally remains undetected until its late states. It may be a form of chronic vascular rejection and when present, ultimately results in left ventricular dysfunction and failure of the graft. The investigators plan to test the hypothesis that vascular tissue, in particular endothelial cells, will reveal abnormalities in metabolism during heart transplant rejection, despite preserved coronary perfusion. The multiple indicator dilution technique will be used to assess adenosine uptake in an isolated rat heterotopic heart transplant preparation. The investigators will compare the endothelial adenosine flux in control syngeneic heart allografts to that of allogeneic rejecting heart allografts. Adenosine flux will also be assessed in a group of allogeneic heterotopic heart transplants from rats treated with cyclosporine and methylprednisolone.